1. Field of the Present Invention
The present invention relates to syringes, and more particularly to a syringe with needle retraction arrangement for automatically retracting the hollow needle into a hollow plunger after use so as to prevent the used needle from contacting with anybody.
2. Description of the Related Arts
It is well known that the needles of syringes are frequently intended for disposal after single use and rendered inoperative to prevent accidental injury or re-use with the substantial risk of cross-contamination.
U.S. Pat. Nos. 4,650,468 and 4,804,370 each suggests a kind of medical syringe that enables its used needle being retracted inside the barrel by re-pulling out the plunger. It is unpractical because the user must apply a pulling force to re-pulling out the plunger that may cause unreasonable danger to the user.
U.S. Pat. No. 4,695,274 discloses an improved kind of medical syringe which further includes a spring inside the barrel. The spring is arranged for automatically re-pulling out the plunger so as to retract the needle inside the barrel. However, the operation becomes much more difficult and troublesome because extra efforts must be applied to retain the needle's working position, i.e. extending out of the barrel.
U.S. Pat. No. 5,084,018 teaches a safety syringe having a sliding base with a hole in a barrel to hold a locking up a fix a needle cannula, in which the hole has a flange at the bottom to prevent downward sliding of the locking tip, the barrel being provided with a plurality of ventilation holes at the front end and a limiting flange at its inner wall to prevent from downward sliding of the sliding base so that the locking tip is positioned for injection, and a spring disposed at the locking tip between an end of the barrel and a needle extender so that when a hollow plunger with a cork at the top is pushed axially to the foremost position, the sliding base is forced to displace forwardly, and consequently the locking tip is forced to keep close contact with the extender and displace in an opposite direction. This kind of safety syringe substantially enables the used needle to be retracted inside the hollow plunger so that no re-pulling operation of the plunger is required. Moreover, a further push of the plunger is required to trigger the retraction of the needle. However, it also contains the following unsolved drawbacks:
(a) Both the sliding base, locking tip and the cork are simply engaged in position by means of limiting flange structure. Such engagement requires high manufacture accuracy to avoid unwanted displacement of the sliding base, the locking tip or the cork during the pushing operation of the plunger for injecting the medical liquid in the barrel. If the sliding base, the locking tip or the cork is not perfectly engaged in position, unwanted disengagement would be resulted during the injection operation that may cause unexpected injury to the patient. In order to ensure all flange engagements, very good quality control is expected and thus the manufacture cost of the 018' patent is relatively higher than usual. Furthermore, since different concentration of the medical liquid may contribute different compressing pressure against the sliding base, locking tip and the cork during the injection operation as mentioned above, a particularly kind of syringe of the 018' patent may only be applied to designated kinds of medical liquid.
(b) The retraction of the needle relies on the inwardly push of the sliding base towards the front end of the barrel, so that a space must be normally retained between the front end of the barrel and the sliding base to receive the sliding base during the retraction operation of the needle. Therefore, a plurality of ventilation holes must be provided at the front end of the barrel for air outlet. It is well known that, during medical injection, air must be absolutely prevented from injecting into a human body. Although high quality of airtight sealing can be provided between the barrel and the sliding base, it is still unreasonable to expose the patient to any kind of such risk.
U.S. Pat. No. 5,782,804 suggests a fluid handling device having a needle retraction assembly which brings about the retraction of a hollow needle after use, wherein a movable sleeve member is provided to substitute the sliding base in the above mentioned 018' patent, and an annular space communicating with outside is formed so that the air space between the sliding base and the front end of the barrel and the air ventilation holes provided on the front end of the barrel as suggested in the 018' patent are eliminated. However, this 804' patent also creates the following new drawbacks at the same time.
(a) As shown in FIGS. 6 and 9 of the 804' patent, some medical liquid will be left in the space formed between the end wall of the piston and the front end of the body portion when the piston is fully pushed before the needle is retracted. In other words, the medicine being actually injected is less than the required dose of medicine.
(b) The engagement between the sleeve member 36 and the needle end portion 18 must be firmer than the engagement between the sleeve member 36 and the annular wall portion 32 of the barrel, so that when the sleeve member 36 is downwardly pressed by the piston 6, the needle end portion 18 will downwardly move with the sleeve member 36 and compress the spring 28, as shown in FIG. 9. However, it is unreasonable that when the sleeve member 36 is pushed to the bottom position as shown in FIG. 10, the spring 28 will push up the needle and the needle end portion 18 to retract upwardly into the hollow piston 6 without driving the sleeve member 36 upwards at the same time.